The present invention generally relates to prosthetic devices, and more particularly to methods and apparatus for forming prosthetic sockets.
Prosthetic devices, such as artificial limbs, typically include a socket into which the remaining portion of a limb is inserted. The socket typically comprises a cup-shaped wall defining a recess into which the remaining portion of the limb is inserted. The socket may be formed by a single piece of rigid material, or may be a composite structure in which a more flexible liner is inserted inside a more rigid outer housing. In either event, several visits to a prosthetist are often needed, during which the shape and/or size of the socket is adjusted, to obtain a socket that fits the limb. Ultimately, a snug fit between the socket and the remaining portion of the limb is desired to maximize comfort to the user.
Unfortunately, several factors may contribute to deteriorate the fit of the socket. Atrophy of the remaining limb portion is a significant factor which contributes to deterioration of socket fit. Atrophy is typically greatest during the initial years of prosthetic use, and often necessitates up to five or more socket re-fittings and adjustments during the first two years. In addition, sockets are typically formed out of a plastic material which is subject to wear. As a result, the other components of the artificial limb typically last much longer than the socket and, therefore, several socket replacements may be required over the life of an artificial limb.
A new socket is typically fabricated using an impression of the original socket. The new socket is formed around the impression, so that the new socket has roughly the same size and shape as the original socket. Previously known methods and apparatus for making a socket impression, however, are overly costly and time consuming, and can introduce inaccuracies and imperfections in the socket duplication process.
For example, a direct plaster method is known in which the original socket is filled with plaster to form a positive plaster impression. The positive plaster impression is then removed from the original socket and used to form a new socket. The shape and geometry of the socket, however, often makes it necessary to cut or otherwise destroy the original socket to remove the positive plaster impression, which is not only wasteful but renders the prosthetic device useless until the replacement socket can be formed. In addition, the plaster must often be repaired, smoothed, and sealed before the new socket can be formed over the positive impression.
Another known method for making a socket impression is the direct plastic approach. In this method, the socket is first treated with a release agent, which is typically messy and generates an undesirable odor as a solvent used with the release agent evaporates. A two-part mixable plastic is poured into the socket, the plastic sets to form a plastic impression of the socket, and the plastic impression is then removed from the socket. The plastic material is flexible, which allows the plastic to be removed, often without requiring the original socket to be altered or otherwise taken apart. It is still difficult, however, to remove the plastic impression from the socket and, therefore, the plastic impression is susceptible to tearing and other deformations. This impression must then be filled with plaster, and a negative plaster wrap is taken and filled in order to create a positive plaster mold. The positive mold is then used to form the new socket. As a result, this method is overly costly and time consuming, and is susceptible to producing inaccuracies in the impression, especially since a second plaster impression is usually required.
A third known method for forming a socket impression is to fill the socket with alginate. The alginate is applied as a thick, viscous material which sets as a gel. The formed gel is then slipped out of the socket and wrapped with a plaster splint to create a positive mold of the socket impression. Plaster is then poured into the negative mold to form a plaster impression about which the new socket is formed. The alginate gel has not been found to accurately retain shape once it is removed from the original socket, and therefore the fit of a new socket formed using this method is often poor. In addition, the method is overly time consuming in that the formed gel is first used to create the positive mold, which is then used to form the plaster impression, before fabricating the new socket.
In each of the above methods, the original socket is coated or filled with a liquid or other flowable material. As a result, any holes or gaps in the original socket must be sealed. Furthermore, the flowable material may still leak through the holes, causing undue mess and requiring additional clean-up time.
While it is often desirable to form a new socket having the exact same size and shape as the original socket, there are many instances in which it is desirable to form a new socket having generally the same shape but a smaller size. As noted above, for example, the remaining portion of the limb may atrophy. To maintain a good fit with the original socket, the user of an artificial limb typically places one or more socks over the remaining portion of the limb to fill in the additional space. The socks must be kept clean and are often cumbersome to use. While a new socket which closely fits the smaller limb size would eliminate the additional gap, the fitting process is protracted and may cause discomfort until the proper adjustments are made. Furthermore, it is not seen how the above-described methods for forming socket impressions would be modified to accommodate the change in limb size.
In accordance with certain aspects of the present invention, a method of forming an impression of a prosthetic socket having an interior surface is provided in which a blank is used. The blank has a wall with an interior surface defining a recess and an exterior surface sized to fit the socket, and is formed of a material which is malleable under low heat and retains flexibility when subsequently cooled. The method comprises the steps of inserting the blank into the socket and heating the blank until the blank is sufficiently malleable. Pressure is exerted on the interior surface of the blank so that the exterior surface conforms to the interior surface of the socket, thereby forming the exterior surface with a molded shape corresponding to the interior surface of the socket. The blank is cooled and removed from the socket, whereby the flexibility of the material from which the blank is formed allows the exterior surface of the blank to deflect slightly during the removing step yet return to the molded shape.
In accordance with additional aspects of the present invention, a method of forming a reduced impression of a prosthetic socket having an interior surface is provided in which a blank is used. The blank has a wall defining an inner cavity and an exterior surface sized to fit the socket, and is formed of a material which is malleable under low heat and retains flexibility when subsequently cooled. The method comprises the steps of inserting a spacer into the socket, the spacer having an interior surface defining a reduced socket recess, and inserting the blank into the reduced socket recess. The blank is then heated until the exterior surface of the blank is sufficiently malleable, and pressure is exerted on the interior surface of the blank so that the exterior surface conforms to the interior surface of the spacer, thereby forming the exterior surface with a molded shape corresponding to the interior surface of the spacer. The blank is cooled and removed from the reduced socket recess. The flexibility of the material from which the blank is formed allows the exterior surface of the blank to deflect slightly during the removing step yet return to the molded shape.
In accordance with still further aspects of the present invention, a blank is provided for forming an impression of an interior surface of a prosthetic socket. The blank comprises a side wall having an exterior surface sized to fit inside the socket, and is formed of a thermoplastic material which is malleable when heated to a low temperature to allow the exterior surface of the side wall to be formed with a molded shape conforming to the interior surface of the socket. The side wall retains the molded shape when cooled, the thermoplastic material having a flexural modulus between approximately 40,000 to 250,000 psi to allow the side wall to temporarily deflect yet return to the molded shape, thereby allowing the blank to be removed from the socket.